Since an electrophotographic technique has an immediacy and can provide images having a high image quality, the technique has recently been widely used in not only the field of copying apparatus but also the field of various printers. Also, as to a latent image holding member (photoreceptor) which is the central part of the electrophotographic technique, inorganic photoconductive materials such as selenium, an arsenic-selenium alloy, cadmium sulfide, zinc oxide, amorphous silicon, etc., have hitherto been used as the photoconductive material but recently organic photoconductive materials which causes no pollution problem and is advantageous in the filming property and the producibility have been variously developed. In these organic latent image holding members, a so-called laminate type organic latent image holding member composed of the laminated layers of a charge generating layer and a charge transport layer has been practically used in many fields owing to the high sensitivity and the long life.
On the other hand, in a two-component developer composed of a positively chargeable toner and a negatively chargeable resin-coated carrier in the electrophotography, fluorine series resins such as a copolymer of vinylidene fluoride and tetrafluoroethylene, a fluoroalkyl methacrylate copolymer, etc., and silicone series resins have been proposed as a resin for coating the carrier in JP-A-61-217068, JP-A-62-24268, and JP-A2-96770 (corr. EP 362650A) (the term "JP-A" as used herein means an "unexamined published Japanese patent application").
Also, JP-A-53-92134 discloses that the surface of a carrier is coated with a chlorinated or brominated vinyl series copolymer and as a monomer for the copolymers, vinylidene chloride is exemplified. However, the technique practically disclosed and used therein is a cascade development only using a carrier coated with a copolymer of vinyl chloride.
These coated carriers have both merits and demerits. For example, it is known that the carriers coated with a fluorine series resin has a good chargeability but some of these carriers have demerits in the charging stability, the adhesion between the coated resin and the carrier core, etc., and also the carriers coated with a silicone series resin also have the foregoing merit but have a demerit that the adhesion between the coated resin and the core is poor and the coated resin is gradually peeled off. Accordingly, these carriers have the demerit of lacking in durability such that the copied images successively formed become unstable and the formation of a background stain (hereinafter, referred to as fog) is gradually increased with repeating the copying procedure using the carrier.
A cascade process was hitherto used for development, but since such the cascade process had the problems that the apparatus using the cascade process was reluctant to be small-sized and the image quality was easily deteriorated due to scattering of toner particles and a so-called edge effect, i.e., a phenomenon that the density of both edges of a fine line formed was increased, a magnetic brush developing process has recently been used.
In the magnetic brush development process, since the surface hardness of an organic latent image holding member is less than that of an inorganic latent image holding member, when, for example, a silicone series resin is used as a coating resin of a carrier at the magnetic brush development, image defects by the abrasion of the magnetic brush is increased with the increase of number of copies. In particular, in half tone images, stripe-like defects are greatly increased. Thus, the use of conventional organic latent image holding members has the demerit of lacking in the durability thereof.